This invention relates to a supply and control device for fluids, e.g. water, under pressure, particularly for use on coffee-making machines and infusion preparing machines in general, but not limited thereto.
As is known, the most critical fluid supply and control conditions are encountered in coffee-making, and more generally infusion-making, machines where any errors in the amount, temperature, and pressure of the fluid supplied immediately reflect in poor machines' performance. Specially critical and important are those devices in such coffee-making machines which inject an amount of water, in predetermined physical conditions, through a charge of coffee or like product which has been ground and loaded into a percolator or "filter".
Two basic types of such devices are currently known, namely a first type wherein water is gravity fed to the coffee charge, and a second type wherein water is pressure forced through the same charge. The latter type is quite advantageous over the former as regards speed of operation, since the pressurized water takes little time to pass through the ground coffee, whereas the non-pressurized water drips through at a very slow rate. However, the pressurized water system has the disadvantage of compacting by pressure action the ground coffee charge to the point of rendering the extraction of coffee oils and essences a difficult and incomplete process. Moreover, the compacting action slows down the hot water flow to a certain extent, thus reducing the advantages afforded by pressure percolation. This behavior is particularly evident in the case of coffee which has been ground into particles of minimal size: in this case, application of excessively high pressure to the coffee powder causes such a high compression of the same that output of liquid coffee from the filter is almost prevented. Specifically, the following phenomenon takes place: initially, by applying pressure water to the coffee powder bed, there is produced a relatively smooth flow of liquid through the coffee charge itself, with attendant extraction of coffee essences, but then the pressure load onto the coffee powder progressively reduces the latter volume, bringing about a concurrent reduction in the percolating water flow as well as in the essence and oil extraction capabilities of the water. Furthermore, as soon as pressure is released, the coffee mass, which is provided with a certain elasticity, expands back at least in part to its former position.
Because of the above-outlined situation, there arises the technical problem of designing a novel pressurized fluid supply and control device, particularly for coffee-making machines, which can overcome the aforementioned difficulties by providing a controlled supply of fluid under pressure, this control capability being more particularly related to fluid temperature, pressure and volume or amount, such as to ensure, for example, a quick and effective percolation of liquid through a powder material, regardless of its particle size.